Articles such as medical instruments and the like are usually sterilized in an autoclave in which the articles are exposed to high pressure saturated steam for a relatively brief interval. Unless the articles are to be used immediately and in close proximity to the autoclave, it is desirable to sterilize the articles while they are inside a valved container as described, for example, in my U.S. Pat. No. 4,748,003.
During the sterilization process, the valves open under the influence of high pressure steam in the autoclave exposing the contents of the container to the hot steam. At the end of the sterilization cycle, when the pressure in the autoclave outside the container is returned to normal, i.e. atmospheric pressure, the valves close so that when the container is removed from the autoclave, the now sterilized articles are maintained in a completely sealed sterile environment until they are needed.
The sterilization container described in the above patent has pressure actuated valves in the top and bottom walls of the sterilization container. Each valve has a large valve opening and a closure therefor, the latter being supported by a bellows capsule mounted inside the container. A return spring mechanism normally maintains the valve closure in its closed position. However, when the pressure outside the container exceeds that within the container by a few pounds per square inch, the force on the valve closure exceeds that exerted by the return spring with the result that the valve closure opens sufficiently to allow high pressure steam to enter the container. That steam collapses the bellows which thereupon moves the valve closure to its fully open position. Both valves being open, high pressure steam can sweep through the container and sterilize the articles therein.
When the pressure inside the autoclave returns to normal after completion of the sterilization cycle, the return spring moves the valve closure of each valve to its closed position thereby sealing the container. As also described in that patent, pressure equalization occurs through a special filter member mounted in the container wall so that a sterile environment at ambient pressure is maintained in the container until the container is opened to remove the articles therefrom.
While the valve described in the above patent operates satisfactorily, it does have certain drawbacks. First and foremost, the bellows capsule has a relatively small diameter in relation to the valve opening and a large length-to-diameter ratio, e.g. 1.3 in./1 in.=1.3. This means that when the valve member starts to open in response to a given pressure differential outside and inside the container and the bellows is collapsed lengthwise, there is a relatively large reduction in the volume of the bellows, i.e. in excess of 20%, and a correspondingly large increase in gas pressure inside the bellows which resists further opening of the valve member.
To avoid this problem, the bellows capsule in the prior value has to be evacuated. This necessitates the use of an elaborate return spring mechanism in order to overcome the increased back pressure and close the valve. Also, the requirement for a bellows that must be evacuated makes the valve somewhat more difficult and expensive to manufacture. In addition, sometimes a small leak may develop in the bellows so that air enters the bellows. Resultantly, during the next sterilization cycle, when the valve member begins to open, that air will be compressed, effectively increasing the spring constant of the bellows so that the valve member does not open as much for a given pressure differential outside and inside the container.